Treatment of a wide range of titanium compounds

ABSTRACT

A process of producing 99% plus titanium dioxide product by using conventional and microwave heating and leaching of the titanium compound feedstock using acid and oxidants. The solid residue from the leaching is used to produce the high quality titanium oxide by froth flotation. Hydrochloric acid can be recovered by multi-stage evaporation. The process can be modified to produce nano-size titanium dioxide product.

FIELD OF INVENTION

This invention is a process to recover high purity titanium oxide from awide range of titanium compounds including rutile ores and sands,ilmenite ores and sands, and by-products of other titanium oxideprocesses and metallurgical processes. This process is simple, lowercapital and operating cost, and environmentally acceptable than existingtitanium oxide processes.

INTRODUCTION

Our company has been successful in developing a process to extractnickel and cobalt from their compounds using microwaves during theleaching process (U.S. Pat. No. 5,665,015, Mar. 16, 1994). Thisknowledge has been used to develop a process for the extraction oftitanium oxide and by-products from their compounds. The process coveredby this patent application is based on about 60 tests using our 3-litremicrowave powered reactor on samples of gravity concentrate rutile oreand titanium oxide tailings.

PRIOR ART

The most popular method of up-grading titanium oxide compounds is afluidized dissolution of the titanium oxide material using chlorine in afluidized bed. The titanium chloride formed is reduced to titanium oxideand the chlorine is recycled to the fluid bed roaster. Aside from theenvironmental consideration, this process is sensitive to the particlesize of the feed so that fines of less than 150 mesh are not acceptable.Further, this process is sensitive to material such as magnesium andcalcium oxides which would deteriorate the quality of the fluid bed. Theresidue from this chlorination process also contains substantial amountsof titanium oxide.

There are existing processes where the titanium oxide compound issubjected to roasting for up-grading of the titanium oxide or roastingfollowed by leaching and recovery of the acid used by pyrolysis. Theroasting of ilmenite to produce a 92.5% titanium oxide product is acommercial process of Tiwest in a plant that has operated for severaldecades in Western Australia.

The leaching of ilmenite with or without prior roasting is described inseveral US patents. U.S. Pat. No. 3,457,037 (Jul. 22, 1969) describes aprocess where the ilmenite is roasted in a reducing atmosphere and thenleached with a mineral acid to dissolve components such as iron andmagnesium. U.S. Pat. No. 3,922,164 (Nov. 25, 1975) describes theup-grading of ilmenite by leaching with hydrochloric acid and a solublechloride such as ferrous chloride, manganese chloride, magnesiumchloride, calcium chloride, and ammonium chloride. Synthetic rutile isproduced from ilmenite by pre-oxidation and reducing roast followed byleaching air and optionally acid and drying is described in U.S. Pat.No. 4,097,574 (Jan. 27, 1978)

A recent process is described in BHP Minerals International applicationPCT/US96/00897 (Jan. 22, 1996) where the ilmenite is subjected to a2-stage leach with strong hydrochloric acid at 25 to 80 C to dissolvethe titanium oxide. After removing the iron as a chloride by cooling thesolution to about 15 C, titanium oxide is precipitated as a fine andhighly pure titanium oxide by hydrolysis at a temperature in excess of75 C. This proposed process has not been successfully commercialized todate.

Total dissolution of the ilmenite requires aggressive leachingconditions such as high pressure and temperature that increases thecapital and operating cost of the process. Further, based on our tests,it is difficult to dissolve the titanium compound completely. Thepresence of impurities such as iron, aluminum, calcium and magnesiuminterfere with the production of the desired pure titanium oxide.

DESCRIPTION OF THE INVENTION

A successful ilmenite process must be friendly to the environment, lowcapital and operating cost, and produce acceptable by-products.

The titanium oxide compound such as an ilmenite or rutile ore, mayrequire some conventional treatment such as crushing, grinding,flotation or magnetic separation or electrostatic separation before theup-graded material is presented as feed to this process.

In one form therefore the invention is said to reside in a process forextracting and producing high-grade titanium oxide from titaniumcompounds consisting of the following steps;

leaching a leach slurry comprising the titanium oxide compound with acidand oxidant using conventional and microwave energy to produce a solidleach residue and a liquid leach residue;

subjecting the solid leach residue to flotation to recover a high gradetitanium oxide concentrate; and

processing the liquid leach residue to recover the acid.

In a further form the invention may be said to reside in a process forproducing highly pure nano-size titanium oxide from titanium compoundsconsisting of the following steps

leaching of the fine titanium compound feedstock with acids and oxidantsusing conventional energy and high temperature microwave energy;

subjecting the leach residue to liquid-solid separation; and

subjecting the clarified leach liquid to hydrolysis to produce nano-sizetitanium oxide.

Hence in one form therefore the invention consists of the followingmajor steps:

1 Leaching of the titanium compound with an inorganic acid such ashydrochloric or sulfuric acid using conventional and microwave energy.

2 Separation of solid and liquid leach residue.

3 Froth flotation recovery of the titanium oxide from the solid leachresidue.

4 Recovery of the acid such as hydrochloric acid and the ironoxide/chloride and other oxides/chlorides by evaporation and lowtemperature control.

In a further form the invention consists of the following major steps:

1 Leaching of the titanium compound at higher temperatures with aninorganic acid such as hydrochloric or sulfuric acid using conventionaland microwave energy.

2 Separation of solid and liquid leach residue.

3 Recovery of titanium oxide by hydrolysis from the liquid leachresidue.

4 Recovery of the acid from the liquid leach residue by evaporation andlow temperature control.

The high purity titanium oxide in excess of 99% purity may be subjectedto calcining, grinding and screening to meet market specifications forpaint pigment grade, smelter feed, and other applications of titaniumoxide.

Lower cost conventional methods are used to up-grade the feed to theprocess of this invention for optimum results in terms of productquality and cost. Such conventional methods may include crushing andgrinding, gravity concentration by spiral concentrators, tables, orjigs; dry or wet magnetic concentration; and by froth flotation. Theoriginal material containing the titanium dioxide may be an ore, a heavymineral sand, or a by-product of a process such as a slag. The materialis generally pre-concentrated to about 35% iron and 35% titanium wherethe mineral is ilmenite and to about 65% titanium dioxide where thematerial is from rutile ore.

Some titanium material may require roasting but this expensive step isgenerally not necessary before the feed material is applied to thisprocess.

Leaching

A pre-leach may be carried out if the titanium compound containssignificant content of vanadium or other valuable base metals.Segregation roasting in reducing or oxidizing atmosphere may be requiredfor efficient recovery of the vanadium. A small quantity of otheroxidant such as hydrogen peroxide may be added to the weak acid solutionfor the extraction of the vanadium. The extraction of precious metalsmay be carried out on the residue of the main titanium oxide leach.Leaching with cyanide solution or electro-leaching is carried out on theleach residue if platinum or gold is to be recovered.

The feed material to the process may be dry or wet but needs to be fine,preferably about minus 20 to 30 microns for an efficient leachingprocess. Acid such as sulfuric acid of about 30 to 60% by weight orhydrochloric acid of about 10 to 30% may be used for leaching. This mayconsist of new acid and re-cycled acid. Cost may decide which acid touse but technically, sulfuric acid may be used where the materialcontains 5 to 20% iron and hydrochloric acid is used in materialcontaining more than 20% iron.

Preferably the leaching is done as counter-current leaching carried outin two or more stages. Conventional heating may be used initially todissolve readily leachable materials followed by the application ofmicrowave energy. Leaching temperature in the leaching tanks ismaintained about 110 C to allow low cost plastic tanks and pipes such asfiber glass or polypropylene to be used. A higher temperature may beused where microwave energy is applied in a series of pipes. The leachslurry exiting the pipes may be cooled before the pressure is releasedthrough the pressure control valve and the wet cyclone.

The intent of the leaching step is to dissolve materials such as oxidesof iron, calcium. magnesium, aluminum, and others. Major materials thatremain un-dissolved include silica, chromite, zircon, and titaniumoxide.

A small amount of titanium may dissolve but this small amount is not aproblem particularly if the leach liquid is re-cycled.

Liquid-Solid Separation

The leach slurry is subjected to a multi-stage wet-cyclone or liquidvortex separation. The solids are passed to a filter for removal of moreliquid and washing on the filter.

The filter may be a disc, drum, pan, or belt filter. The washed solidsare transferred to the flotation concentration step while the liquid isstored in the weak acid storage.

The liquid leach solution is stored prior to the acid recovery step.

Froth Flotation Up-grading of Titanium Oxide

The leach solid residue is re-pulped in recycled flotation liquid. ThepH is adjusted to between 8 and 10 with soda ash or lime. Frothers suchas pine oil and collectors such as oleic acid are mixed with the slurry.Roughing-and cleaning flotation is applied to the slurry. A high gradetitanium oxide is recovered at high recovery in the flotationup-grading.

Tests have been carried out on a gravity concentrate of a South Americanlow-grade rutile ore using a 3-litre reactor powered by a 1.2 kilowattsmicrowave generator and electrical heating coils to provide conventionalheating. Sulfuric acid was used in these tests due to the low ironcontent. The results of the test are shown in Table 1. TABLE 1 TestResults on Rutile Ore Product Wt.-grams TiO₂ % ppm Distribution %Leaching Leach Residue 248.92 61.2 95.15 First Leach Product 2.70 13.30.23 Second Leach Liquid 3,400 2,177 ppm 4.62 Calculated Head 297.2 52.5100.00 Flotation Cleaner Concentrate 74.30 99.2 97.2 Cleaner Tailings7.03 14.7 1.4 Rougher Tailings 42.62 2.57 1.4 Calculated Head 123.9561.2 100.00

Without the leaching step for this rutile ore, the best grade achievedby a research group in Canada is 89.2 percent TiO₂. This grade oftitanium dioxide is not saleable.

The flotation up-grading of this process may be used to up-grade leachresidues from other processes such as the Tiwest process of reductionroasting of ilmenite and leaching with ammonium chloride.

The total recovery of titanium dioxide from the up-graded gravityconcentrate feed is about 92.5 percent. The high grade titanium oxideflotation concentrate may further be treated by calcining, sizereduction by vortex grinding, and screening to separate fractions forsale as paint pigment feed, smelter feed, welding rod coating, and otherindustrial and pharmaceutical uses.

Residue from the flotation concentration contains substances such assilica, chromite, zircon, and thorium. The chromite can be recovered bymagnetic separation while the zircon and other heavy minerals may berecovered by gravity separation methods.

Recovery of Acid and By-products

The usual method of recovering acid is by pyrolysis and this may be usedin this process if sulfuric acid is used but the preferred method ofthis process is by evaporation where the acid used is hydrochloric acidbecause hydrochloric acid is volatile.

Laboratory test on liquid leach residue showed that hydrochloric acidcan be removed from the leach liquor residue by evaporation. Evaporationmay be carried out in a multi-stage operation. The evaporated acid maybe recovered by condensation for re-cycle to the process.

Laboratory test also showed that as the hydrochloric acid is removed,oxides/chlorides of iron, magnesium, aluminum, and calcium areprecipitated. Laboratory tests also showed that some degree ofseparation of these oxides/chlorides may be achieved by cooling theresidue of evaporation at different temperatures down to about minus 10C.

The liquid leach residue may also be subjected to cyanide orelectro-leaching to recover precious metals such as platinum.

Where the acid is sulfuric acid, the sulfuric acid may be recovered bypyrolysis of the liquid leach residue. The use of counter-currentleaching method and microwave energy reduces the acid addition to theprocess.

The process described above applies to the production of industrialgrade titanium oxide for use in paint, smelting, and welding industries.The process of this invention can also be used to produce nano-sizetitanium dioxide. Laboratory test using the 3-litre microwave poweredreactor showed that it is possible to dissolve the titanium oxide byusing temperature higher than 110 C. After separating the solid leachresidue, very fine titanium oxide (nano-size) precipitate is produced byhydrolysis and then lowering the temperature of the liquid to aboutminus 10 C.

It is advantageous to use high grade titanium oxide feed in producingthe nano-size titanium oxide material. Higher strength acid with highertemperature with microwaves is required to dissolve the titanium oxidefeed in the leaching process. This is economically possible in acommercial operation when the leaching set-up shown in FIG. 1 is used.

The process of this invention or parts of it may be used to recoveradditional high grade titanium oxide from the reject of other titaniumoxide processes such as the chloride roasting process or to up-grade thetitanium oxide produced from processes such as the Tiwest reductionroasting and leaching with ammonium chloride. In the Tiwest process,size reduction and froth flotation of the titanium oxide concentratewill result in higher grade of the titanium oxide product.

BRIEF DESCRIPTION OF THE DRAWINGS

A description of the drawings is given below to further describe theembodiments of the invention.

In the drawings:

FIG. 1 shows a flow sheet of one embodiment of this invention for atwo-stage method of conventional heat and microwave leaching in countercurrent mode according to this invention;

FIG. 2 shows a flow sheet of an embodiment of this invention for thetreatment of concentrated ilmenite or up-graded rutile ore; and

FIG. 3 shows a flow sheet of an embodiment of this invention for aprocess to recover titanium oxide from chlorination process tails.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a diagram showing a two-stage method of heat and microwaveleaching in counter current mode according to this invention.

Up-graded titanium oxide feed 1 is introduced into the leaching tank 2fitted with agitator 3 with the liquid 16 from the next leaching stage.The small addition of acid and reagents is shown by 17. Conventionalheat or microwave energy is used to maintain the temperature of theleach tank 2 at about 110 C. Readily leachable material is leached inthe tank. The slurry 4 is pressurized by pump 5 and delivered to pipereactor 6 fitted with microwave generator, wave guide, and window 7 and8 at both ends of the pipe. There may be several pipe reactors connectedin series. The discharge of the leach slurry is controlled by thepressure control valve 11 before the slurry is passed to the liquidvortex or wet cyclone 12. If required, slurry 14 is cooled beforepassing through control valve 11. The liquid 13 is passed on to theprior leaching stage while the solids 15 is passed on to the nextleaching stage.

Microwave energy may be applied at the bottom of the leaching tank butthe preferred method of applying the microwave in the pipe reactors isshown on FIG. 1 where the slurry is pressurized by a pump to a series ofpipes where microwave energy is applied. The pipes may be made of steelor stainless steel coated with plastic such as PTFE. Internal bafflesmay also be installed in the pipe to ensure mixing of the slurry as itis presented to the microwaves. This preferred method allows higherpressure and temperature to be used during the microwave leachingwithout overly increasing the cost.

The leaching process may be carried out in two or more stages.

FIG. 2 is an embodiment of this invention for the treatment ofconcentrated ilmenite or up-graded rutile ore. Sulfuric acid orhydrochloric acid may be used.

Feed 20 consisting of concentrated ilmenite or up-graded rutile frombeach sand or a rutile ore body, is mixed in a tank 21 with recycledliquid 23 and acid/reagents 22. The slurry 24 is then passed on to thefirst stage leach tank 25 where conventional heat 26 is applied to atemperature of about 110 C to dissolve readily soluble material andutilize the acid as much as possible. The first stage leach slurry 27 ispassed to a vortex separator or wet-cyclone 28 where as much of thesolids 30 are separated from the liquid 29. There may be several stagesof vortex separators. The liquid is passed to a storage tank orthickener 33 prior to acid and oxide recovery. The solid 30 is passed tothe second stage leach tank 31 where recycle acid liquor 78 and acid isadded 32. The slurry 36 is pressurized by a pump 37 and passed through aseries of pipes 38 fitted with wave guides and magnetrons at the ends ofthe pipes to deliver microwave energy to the slurry. The pipes areinternally coated with chemical resistant material such as PTFE andheating coils are installed outside of the pipe to control thetemperature. Baffles are also installed inside the pipe to ensureturbulent presentation of the slurry to the microwaves. The treatedslurry is passed through a pressure control valve 39 before feeding to awet cyclone or liquid vortex separator 40. If required, the treatedslurry is cooled before passing to the pressure control valve 39. Theremay be additional leaching stages as required by the particular materialbeing treated.

Some fresh water may be added at this time to precipitate some of thedissolved titanium by hydrolysis. Only a very small amount isprecipitated.

The leached slurry is passed through a series of wet cyclone or liquidvortex separators 40 to separate the solids 41 from the liquid 23. Theliquid 23 is returned to the previous leaching stage 21 and the solids41 are fed to a belt filter 42. Liquid 43 from the first section of thebelt filter is returned to the previous leach stage 21 while the solidsis washed in the next section of the belt filter 42 with wash water 43.Wash solution 72 joins the acid water re-cycle. Washed cake 45 from thesecond section of the filter is repulped with re-cycle liquid 47 andflotation reagents 48 are added in mixing tank 46. The slurry is thensubjected to rougher and cleaner flotation 49 yielding a floatconcentrate 59 and a flotation tailings 50.

The flotation concentrate 59 is high-grade titanium oxide of 99% plusTiO₂ obtained at high recovery and is subjected to liquid-solidseparation 60. The liquid 61 is re-cycled to the mixing tank 46 and thesolids 62 are calcined 63 and the calcined product 64 is ground in avortex grinder 65. The ground product 66 is screened 67 to separatepaint pigment grade 68, smelter grade 69, welding coating grade 70, andother applications 71.

The flotation tailings 50 are passed through high intensity magneticseparation 51 to recover the chromite 53. The magnetic tailings 52 aresubjected to gravity separation 54 to recover heavy minerals includingzirconium, gold, and platinum 55. The final tailings 56 containingmostly silica is subjected to liquid solid separation 57 where theliquid 47 is returned to the flotation mixing tank 46 and the solids 58are delivered to the waste pond.

Primary leach liquor 35 stored in storage thickener 33 is passed to amulti-stage evaporation system 73 where the hydrochloric acid is removedfrom the leach liquid 35. As acid is removed, the oxides/chlorides ofiron, magnesium, calcium, aluminum and sodium 75 are precipitated. Ifeconomically desirable, the different oxides may be separated byreducing the temperature in stages to minus 10 C. The by-products,particularly iron oxide, may be sold to consumers after drying andcalcining.

The vapour 74 from the multi-stage evaporator is passed to a condenser76 to recover the acid 77 and re-cycle 78 to the leach process.

The process of this invention may also be used to recover significantamounts of titanium oxide from the residue of other titanium chlorideprocesses in particular the predominant titanium oxide fluidizedchlorination process. The tailings from this chlorination processcontains fine particles that are rich in fine titanium oxide.

The process to recover titanium oxide from the chlorination tails isgiven in FIG. 3.

Residue 91 is recovered from the tailings pond 90 and subjected to wetor dry grinding 92. Reagents and re-cycled liquid 94 is added before theslurry 93 is subjected to primary flotation and magnetic separation 95to recover an up-graded titanium oxide concentrate 97. Theflotation-magnetic treatment 95 will up-grade the titanium oxide fromabout 20% to about 60% TiO₂. The tailings 96 from the flotationoperation-magnetic separation 95 are returned to the tailings waste pond90.

The titanium oxide flotation-magnetic concentrate 97 is subjected toliquid solid separation 98 using vortex separators and filtration beforeleaching with acid in a counter-current microwave assisted leaching 102with hydrochloric acid 101 added as described in FIG. 1. The leachslurry 103 is subjected to liquid-solid separation and filtering andwashing 104. The washed solid residue 105 is subjected to flotationseparation to produce a high grade titanium dioxide concentrate 109 anda waste residue 108 that is delivered to the waste pond.

The high grade titanium dioxide concentrate 109 is subjected to liquidsolid separation 110 before calcining 112 to produce a high gradetitanium oxide product.

The liquid 114 from the leach process is passed to the multi-stageevaporation system 115 where oxides/chlorides are precipitated and theacid vapor 117 is produced. The oxides/chlorides 116 are returned to thewaste tailings pond while the evaporated fumes 117 are passed to acondenser 118 to recover the acid 119 for re-cycle to the leachingprocess.

1. A process for extracting and producing high-grade titanium oxide fromtitanium compounds consisting of the following steps; leaching a leachslurry comprising the titanium oxide compound with acid and oxidantusing conventional and microwave energy to produce a solid leach residueand a liquid leach residue; subjecting the solid leach residue toflotation to recover a high grade titanium oxide concentrate; andprocessing the liquid leach residue to recover the acid.
 2. A process asin claim 1 wherein the titanium compound is ground fine to about 20microns.
 3. A process as in claim 1 wherein the acid used for leachingis an organic acid selected from the group sulfuric acid, nitric acid orhydrochloric acid.
 4. A process as in claim 1 wherein the acid issulfuric acid and is used in a concentration of 30 to 60% w/w.
 5. Aprocess as in claim 1 wherein the acid is hydrochloric acid and is usedin a concentration of 10 to 30% w/w.
 6. A process as in claim 1 whereinthe oxidant is hydrogen peroxide.
 7. A process as in claim 1 whereinconventional heat energy is applied to the leaching step to maintain aleaching temperature up to 110 C.
 8. A process as in claim 1 whereinmicrowave energy is applied to the leaching step with the leachtemperature at a maximum of about 110 C when applying microwave to aleach tank.
 9. A process as in claim 1 wherein the microwave energy isapplied to the leach slurry at higher temperature and pressure through aseries of pipes fitted with microwave generators.
 10. A process as inclaim 1 wherein the leaching step is carried out as a counter currentprocess to reduce the addition of the acid.
 11. A process as in claim 1where the solid leach residue is separated from the liquid leach residueand washed.
 12. A process as in claim 10 wherein the washed solid leachresidue is mixed with re-cycled liquid and the pH adjusted to between 8and 11 with soda ash or lime.
 13. A process as in claim 1 whereinflotation frother and collector reagents are mixed with the solid leachresidue in the flotation step.
 14. A process as in claim 1 wherein theflotation concentrate is high grade titanium oxide and the flotationtailings are insolubles such as silica, chromite, and zirconia.
 15. Aprocess as in claim 13 wherein the flotation concentrate is subjected toliquid-solid separation, calcining, size reduction and screening toproduce various grades of titanium oxide products.
 16. A process as inclaim 13 where the flotation tailings are subjected to magnetic andgravity separation to extract by-products including chromite, zirconiaand precious metals such as gold or platinum.
 17. A process as in claim1 wherein the titanium oxide compound contains vanadium and comprising afirst step of oxidation or reduction roasting.
 18. A process as in claim17 wherein a pre-leach with acid and hydrogen peroxide is carried out onthe roasted titanium compound to extract vanadium.
 19. A process as inclaim I wherein the solid leach residue is subjected to cyanide orelectro-leaching to recover precious metals such as platinum.
 20. Aprocess as in claim 1 wherein the acid is hydrochloric acid and theliquid leach liquor residue is subjected to a multi-stage evaporation torecover the hydrochloric acid.
 21. A process as in claim 20 whereinvapor from the evaporation vapor is condensed to recover thehydrochloric acid.
 22. A process as in claim 20 wherein cooling of theresidue liquid from evaporation results in the precipitation of theseveral oxides/chlorides such as iron, magnesium, vanadium, aluminum,calcium oxide.
 23. A process as in claim 1 wherein the acid is sulfuricacid and the sulfuric acid is recovered by pyrolysis of the liquid leachresidue.
 24. A process for producing highly pure nano size titaniumoxide from titanium compounds consisting of the following steps leachingof the titanium compound with acid and oxidants using conventionalenergy and high temperature microwave energy; subjecting the leachresidue to liquid-solid separation to produce a solid leach residue anda liquid leach residue; subjecting the clarified liquid leach residue tohydrolysis to produce nano-size titanium oxide; and processing theliquid leach residue to recover the acid.
 25. A process as in claim 24wherein the titanium compound feed is greater than 90 percent titaniumoxide.
 26. A process as in claim 24 wherein the leaching with microwaveenergy is carried out at a temperature greater than 110 C but less than180 C to dissolve the titanium compounds.
 27. A process as in claim 24wherein the acid is sulfuric acid and is used in a concentration ofabout 30 to 60% w/w.
 28. A process as in claim 24 wherein the acid ishydrochloric acid and is used in a concentration of about 10 to 30% w/w.29. A process as in claim 24 wherein the leaching step is carried out asa counter current process to reduce the addition of the acid.
 30. Aprocess as in claim 24 wherein the solid leach residue is rejected towaste.
 31. A process as in claim 24 wherein the leach liquid residue issubjected to hydrolysis and temperature control with or without seedingof titanium oxide particles, to precipitate nano-size titanium oxideparticles.
 32. A process as in claim 31 wherein the precipitate isseparated from the liquid and subjected to calcining, vortex grinding,and screening to produce nano-size titanium oxide product.
 33. A processas in claim 24 wherein the acid is hydrochloric acid and the liquidleach residue is subjected to a multi-stage evaporation to recover thehydrochloric acid.
 34. A process as in claim 33 where the vapor from theevaporation stage is condensed to recover the acid for re-cycle.